Moseley was born into slavery in Goochland County about 1819 or 1820. Family tradition does not preserve the names of his parents. According to that tradition, he belonged to a member of the Haden family and his owner allowed or enabled him to operate a boat on the James River before the Civil War. The absence of Moseley’s name from census returns, from the Goochland County Free Negro Register, and from almost all other local records suggests that he did not constantly reside in the county, but a boatman probably would have resided on his boat. Moseley was free by 1857 when he married Martha Catherine Turpin, the recently freed daughter of a white planter, Edwin Turpin, and his enslaved woman Mary James. They had at least seven sons and six daughters by 1880. Her brotherserved in the House of Delegates.
While Moseley apparently operated his boat on the James River, his wife and children resided with her father and siblings. In November 1863 when Moseley purchased three lots in the town of Columbia in Fluvanna County on the western border of Goochland County for $3,000—probably in depreciated Confederate currency—the deed identified him as a resident of the city of Richmond. The purchase demonstrates that Moseley had been successful in his business. He attended a convention of African Americans in Alexandria in August 1865 as a delegate from Goochland County. In October 1866, however, when he purchased part interest in 4.78 acres of land in Henrico County just east of the city boundary, the deed identified him as still a Richmond resident. Moseley returned to Goochland County soon thereafter. In March 1867 the county agent of the Bureau of Refugees, Freedmen, and Abandoned Lands placed Moseley’s name first in a list of six of the most-influential African Americans in the county. A writer for the National Anti-Slavery Standard described Moseley in 1869 as “a large, benevolent-looking” man with “iron-grey whiskers” and reported that he was educated but “makes no display of his intelligence.”
On October 22, 1867, Moseley received 75 percent of all the votes cast in Goochland County to win election over two white candidates to represent the county in the convention that met in Richmond from December 3, 1867, through April 17, 1868, to write a new state constitution. All of Moseley’s 1,284 votes came from African Americans. The president of the convention appointed Moseley to the very important Committee on the Elective Franchise and Qualifications for Office but subsequently reassigned him to the Committee on Military Affairs. Moseley voted for almost all the important reforms the convention adopted, including suffrage and full equal rights for African Americans, disfranchisement of most former Confederates, and creation of the state’s first system of free public schools.
In July 1869, when voters ratified the constitution and stripped disfranchisement of former Confederates out of it, Moseley easily defeated a white Conservative Party candidate 3,252 to 2,388 to represent the counties of Fluvanna, Goochland, andin the Senate of Virginia. Unfriendly newspaper reports described him as a radical, and he was appointed to the lowest-ranking seat on the Committee on Banks. During the first short session of the assembly in October 1869, he missed the vote to ratify the but voted later in the same day to ratify the to the U.S. Constitution as Congress required before it admitted senators and representatives from Virginia to their seats. On June 7, 1870, Moseley offered an amendment to the public school bill to prohibit racial segregation, but it failed to pass. He did not vote when the bill requiring segregated schools passed and subsequently presented a protest that the senate refused to publish in the printed journal. However radical Moseley was on matters relating to African Americans and their rights, he nevertheless joined most of the other African American members of the assembly and a majority of white members in voting for the Funding Act of 1871 that refinanced the , which became one of the most controversial acts of that assembly.
The new constitution set senators’ terms of office at four years but provided that half the senators elected in 1869 serve two-year terms in order that thereafter half the senators be elected every second year. Moseley’s district was one of the two-year term districts. He evidently did not seek the nomination in 1871 after senatorial districts had been reconfigured to place Goochland County in a district with Powhatan and Chesterfield counties. Instead, he sought thenomination for the Goochland County seat in the House of Delegates, but in what appears to be a compromise between factions of the party, his brother-in-law Henry Turpin received the nomination.
Moseley was active in Republican Party politics throughout the 1870s and served on the resolutions committee of the 1870 state convention. A meeting of African Americans in Richmond in April 1872 elected him and seven other men to represent the state at a national convention of African Americans. In 1873 Moseley sought the Republican nomination for state senate, but in October announced that he would run as an independent Republican. He indicated, however, that if a Conservative candidate entered the race he would withdraw so as not to split the Republican ticket, which he evidently did since another Republican was elected. Moseley was a delegate to state conventions of African Americans in April 1875 and August 1875. He announced his availability for the Republican Party nomination for the House of Representatives in 1880, but John Paul, a, ran with Republican support and won.
When Moseley was a member of the Convention of 1867–1868, he had been described as a farmer, rather than as a boatman. In addition to the three town lots in Columbia and the property in Henrico County, he then owned only four head of taxable livestock in Goochland County. Following his father-in-law’s death in 1868, Moseley and his wife purchased three tracts of land from the estate with him as trustee for her and their children. The property in the western part of Goochland County encompassed almost five hundred acres of land and had a taxable value when they finished paying off the note in 1883 of almost $1,800. To keep up the payments, Moseley borrowed money from two of his brothers-in-law. He had to sell a brick house in Richmond he had acquired through his wife and in-laws, as well as the three town lots in Columbia. He was not able to collect the money for the three lots, however, and initiated a lawsuit in 1876 that his children continued prosecuting until it was settled in 1901. Moseley and his family apparently resided on the Turpin family property in Goochland County, but Moseley family tradition indicates that he lived in the Haden family’s former house. Following Moseley’s death, creditors of Edwin Turpin’s estate successfully sued to have the land sold. Moseley’s wife died on January 24, 1890, and William P. Moseley died at his home in Goochland County on August 17, 1890. The place of his burial is not known.